(a) Field of the Invention
The present invention relates to a method and apparatus for receiving data and method for transmitting data in a mobile communication system, and more particularly, to an apparatus and method for receiving data and method for transmitting data which can improve transmission efficiency.
(b) Description of the Related Art
In an LTE (Long Term Evolution) system, one frame consists of 10 subframes, each subframe consists of two slots, and each slot consists of 6 or 7 symbols depending on the length of a CP (cyclic prefix). TTI (Transmission Time Interval), a data transmission unit, is 1 ms, which is equal to the length of a subframe.
In the frequency domain, an uplink subframe, which is used in the LTE system, is divided into a control region where PUCCH (Physical Uplink Control Channel) is allocated and a data region where PUSCH (Physical Uplink Shared Channel) is allocated. In the uplink, reference signals (RS) are not precoded as opposed to data, and include DMRSs (Demodulation RS) and SRSs (Sounding RS). The DMRSs are reference signals used to obtain channel information for uplink data demodulation, and the SRSs are reference signals used to measure the uplink channel.
In order for 5th generation communication systems to provide more diverse services than 4th generation communication systems, a low-delay technology is required which enables data exchange between a base station and a terminal within a short time.
In LTE systems, the time required for transmission in a wireless zone is as much as 1 ms, thus, it is necessary to reduce the length of the TTI for low-delay purposes. Also, as far as HARQ (Hybrid Automatic Repeat Request) is concerned, it is necessary to reduce the demodulation time after the base station or terminal receives a signal. For example, suppose that the TTI has a length of x ms and a HARQ re-transmission is made after three TTIs, the allowable maximum demodulation delay is 3×. A reduction in the TTI length increases the DMRS overhead (ratio between the number of data subcarriers and the number of DMRS subcarriers) for maintaining the same channel estimation performance, and a reduction in DMRS overhead may deteriorate the channel estimation performance. For example, in the case of the TTI consists of two symbols, a DMRS corresponding to one symbol is required to achieve the same channel estimation performance as the TTI is 1 ms and intra frame hopping is applied. In this instance, the DMRS overhead increases from 14%, which is obtained for a TTI of 1 ms, to 50%. Moreover, the requirements for reduction of demodulation delay set limits on the positions of PUSCH and PUCCH in resource elements including subcarriers and symbols, which may result in performance deterioration.
For example, in a case where the TTI consists of two symbols and a DMRS is allocated at the first symbol in order to reduce the demodulation delay, channel estimation can be done as long as the first symbol is received, and the time required for channel estimation can be reduced. Thus, the demodulation delay can be reduced. However, there is a difference in the number of data subcarriers used between the first symbol and the second symbol. This disables symbol hopping, and therefore causes performance deterioration. In addition, in the case of systems for which low-delay is an important issue, SC-FDMA (Single-carrier Frequency Division Multiple Access) adapted in LTE systems can improve PAPR (peak-to-average power ratio) but causes demodulation delay.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.